Introduction to Network DesignNetwork EvaluationExample 1Cheap Network (by Intrepid)Messy NetworkRank Designs by AttributesJustify the DesignsCompare DesignsWhat is more important, Performance or Cost?Two-Location ProblemCost of Network Services and ComponentsPublic Switched Telephone Network SolutionCost of PSTN SolutionUtilization AnalysisDesign Principle 2.1PBX SolutionReducing Trunks at BregenFamous 2 camel hump Telephone Traffic Daily PatternErlang: the Traffic Measure UnitErlang CalculationQueueing Theory for System with LossM/M/2 QueueLoss with m Lines (m servers, no queue)Erlang-B FunctionCalculating the BlockingDesign Intersite LinkSimplified Traffic ProfileReduce Cost by Using Leased LinesBusy Hours Analysis for Leased Line Saving2nd Leased Line SavingOff-Peak Analysis of 3rd Leased LineFinal DesignCost of Final DesignHomework #101/13/19 C. Edward ChowCS622 Page 1Introduction to Network DesignNetwork design is •Create network structure (blue print)•Decide how to allocate resource and spend moneyTwo basic questions:•How much it cost to build a usable network?•How much improvement does $x buy?Answer:•Depend on network services and components available•We will concentrate the techniques and algorithms01/13/19 C. Edward ChowCS622 Page 2Network Evaluation•Every network has three characteristics:–Cost–Performance–Reliability•First we need to find agree-upon quantitative numbers.•Based on the quantitative numbers of these characteristics, we can evaluate different design alternative by ordering them and ruling out losers.01/13/19 C. Edward ChowCS622 Page 3Example 1•Four designs for a network design problem01/13/19 C. Edward ChowCS622 Page 4Cheap Network (by Intrepid)01/13/19 C. Edward ChowCS622 Page 5Messy Network01/13/19 C. Edward ChowCS622 Page 6Rank Designs by Attributes01/13/19 C. Edward ChowCS622 Page 7Justify the Designs•There can be factors that decides the final choice:Whether the company is expanding•Maybe the proposed designs are not as expected.•In outsourcing situation, you may ask for redesign•You may not have to serve as designer but as an evaluator.01/13/19 C. Edward ChowCS622 Page 8Compare Designs01/13/19 C. Edward ChowCS622 Page 9What is more important, Performance or Cost?•150 cashiers $13,725/month•CEO  $152,500/month•One user my justify the building a high performance network01/13/19 C. Edward ChowCS622 Page 10Two-Location Problem•It is called “Hello World” of Network Design.•It is undaunting yet interersting problem!•Design a network connecting two locations, 200km apart.•Anagon city with 5 employees, Bregen with 10.•Each employee –call other site 4 times/day, avg. 5 min. each.4*5*15=300 min/day–call others in the same office 10 times/day about joint work, each last avg. 3 min. 10*3*15=450 min/dayNote here we are not using C(10,2)+C(5,2) for the # of calls•How can we best provide the communications between the two cities01/13/19 C. Edward ChowCS622 Page 11Cost of Network Services and Components•Network equipment purchase is typically amortized at 3% per month.•The PBX Private Branch Exchange would cost $60/month01/13/19 C. Edward ChowCS622 Page 12Public Switched Telephone NetworkSolution01/13/19 C. Edward ChowCS622 Page 13Cost of PSTN SolutionAssume 21 2/3 work days=65/3 daysLocal call: 450min/day*0.05$/min*65/3day=487.5$Long distance call; 300min/day*0.4$/min*65/3day=2600$01/13/19 C. Edward ChowCS622 Page 14Utilization Analysis•5 employees at Anagon place 4*5min*5=100 min calls/day to Bregen•10 employee at Bregen place 4*5min*10=200 min calls/day to Anagon•300 min long distance calls are shared among 5 employee at Anagon.•That is 300min/5=1 hour/employee/day on long distance.•For 8 hour day, each phone at Anagon is busy 25%=2/8? of the time. While phone at Bregen is busy 18.75%=1.5/8? Low Utilization•Resaon: Each employee at Anagon makes 10*3min/day=30min local call, but it will tie up other employee’s line. Assume no conference call. Therefore each line is 30min*2=1hour/day is busy on local call.01/13/19 C. Edward ChowCS622 Page 15Design Principle 2.1•Good network designs tend to have many well-utilized components.01/13/19 C. Edward ChowCS622 Page 16PBX Solution$487.5/month for local calls savedWith$60*2=$120 amortized PBX cost, we actually save $367.5/monthReliability degraded?!Performance?01/13/19 C. Edward ChowCS622 Page 17Reducing Trunks at Bregen•There can be 5 intersite simultaneous calls.•Reduce 10 outgoing trunks at Bregen to 5.•$25/month*5=$125/month access fee saving.•How can we reduce the cost further?•Clue Study the usage pattern01/13/19 C. Edward ChowCS622 Page 18Famous 2 camel hump Telephone Traffic Daily Pattern•Traffic measured in Erlangs.01/13/19 C. Edward ChowCS622 Page 19Erlang: the Traffic Measure UnitDefinition 2.1If call arrive rate=and departure rate=,Then the call intensity is E= Erlangs.In honor of Danish Telephone engineer Erlang.Example 1. Calls arrive 2 per min., and hold for an average of 3 min, then=2 and  =3, E=  =6 Erlangs.Note that hold time (H)= 1/departure rate; H=1/.Apparently one line cannot handle this amount of traffic.When a call comes and all lines are busy, the call is blocked.How many lines can reduce the blocking probability to x%?01/13/19 C. Edward ChowCS622 Page 20Erlang Calculation•In our 2-location case, 15 places 4 long distance calls/day, each call last avg. 5min. Assume 8 hr day•What is the call (traffic) intensity for the day?=15*4 calls/8 hr = 15/2 calls/hrH=5 min/call =1/12 hr/call=1/H=12 calls/hr = 0.2 calls/minE==(15/2)/12=15/24=5/8 Erlangs.•Assume 20% of the traffic in the busy hour. What is the call intensity in the busy hour?=60 calls/day * 0.2 = 12 calls/hr = 0.2 calls/min=1/H=12 calls/hr = 0.2 calls/minE==12/12=1 Erlang.01/13/19 C. Edward ChowCS622 Page 21Queueing Theory for System with Loss•Assume a telephone system with multiple lines.–When a call comes and all lines are busy, the call is blocked. Unlike data network, calls are not buffered or queued if lines are not available.–Or, you can consider it is a finite queue, i.e., after queue full (line busy), further call are blocked.How many lines can reduce the blocking probability to x% for a given traffic density?•Queueing theory can be used analyzed the telephone system’s performance, specifically the blocking